Polyvinyl alcohol and method for producing same

Abstract

A polyvinyl alcohol is produced in a method comprising: a polymerization step comprising polymerizing vinyl ester monomers by controlled radical polymerization in the presence of a radical initiator and an organic cobalt complex to obtain a polymer solution containing a polyvinyl ester; an extraction step comprising extracting a cobalt complex from the polymer solution by contacting an aqueous solution containing a water-soluble ligand with the polymer solution; and a saponification step comprising saponifying the polyvinyl ester after the extraction step to obtain a polyvinyl alcohol. A method for producing a polyvinyl alcohol is thus provided that has a narrow molecular weight distribution and a high number-average molecular weight with good hue and further good solubility in water.

The invention claimed is: 
     
       1. A method for producing a polyvinyl alcohol, the method comprising:
 polymerizing vinyl ester monomers by controlled radical polymerization in the presence of a radical initiator and an organic cobalt complex to obtain a polymer solution comprising a polyvinyl ester; 
 extracting a cobalt complex from the polymer solution by contacting an aqueous solution comprising a water-soluble ligand with the polymer solution; and 
 saponifying the polyvinyl ester after the extracting to obtain the polyvinyl alcohol; 
 wherein the polymerization is bulk polymerization or solution polymerization. 
 
     
     
       2. The method of  claim 1 , wherein the polyvinyl ester after the extracting has a cobalt element content from 0.01 to 100 ppm. 
     
     
       3. The method of  claim 1 , wherein the polyvinyl alcohol after the saponifying has a cobalt element content from 0.01 to 50 ppm. 
     
     
       4. The method of  claim 1 , wherein the water-soluble ligand is an acid having a pKa at 25° C. from 0 to 12. 
     
     
       5. The method of  claim 1 , wherein the water-soluble ligand is a carboxylic acid. 
     
     
       6. A method for producing a polyvinyl alcohol, the method comprising:
 adding vinyl ester monomers, a radical initiator and an organic cobalt (II) complex to a reactor; 
 polymerizing the vinyl ester monomers by controlled radical polymerization in the reactor to obtain a polymer solution comprising a polyvinyl ester; 
 extracting a cobalt complex from the polymer solution by contacting an aqueous solution comprising a water-soluble ligand with the polymer solution; and 
 saponifying the polyvinyl ester after the extracting to obtain the polyvinyl alcohol. 
 
     
     
       7. The method of  claim 6 , wherein the polyvinyl ester after the extracting has a cobalt element content from 0.01 to 100 ppm. 
     
     
       8. The method of  claim 6 , wherein the polyvinyl alcohol after the saponifying has a cobalt element content from 0.01 to 50 ppm. 
     
     
       9. The method of  claim 6 , wherein the water-soluble ligand is an acid having a pKa at 25° C. from 0 to 12. 
     
     
       10. The method of  claim 6 , wherein the water-soluble ligand is a carboxylic acid. 
     
     
       11. A method for producing a polyvinyl alcohol, the method comprising:
 polymerizing vinyl ester monomers by controlled radical polymerization in the presence of a radical initiator and an organic cobalt complex to obtain a polymer solution comprising a polyvinyl ester; 
 extracting a cobalt complex from the polymer solution by contacting an aqueous solution comprising a water-soluble ligand with the polymer solution; and 
 saponifying the polyvinyl ester after the extracting to obtain the polyvinyl alcohol, 
 wherein the radical initiator is selected from the group consisting of azo initiators, peroxide initiators and redox initiators. 
 
     
     
       12. The method of  claim 11 , wherein the polyvinyl ester after the extracting has a cobalt element content from 0.01 to 100 ppm. 
     
     
       13. The method of  claim 11 , wherein the polyvinyl alcohol after the saponifying has a cobalt element content from 0.01 to 50 ppm. 
     
     
       14. The method of  claim 11 , wherein the water-soluble ligand is an acid having a pKa at 25° C. from 0 to 12. 
     
     
       15. The method of  claim 11 , wherein the water-soluble ligand is a carboxylic acid.